Wastewater COD Too High? 5 Common Sources of the Problem in Factories

A sudden high COD lab result often makes factory owners anxious. This is understandable, because COD levels that exceed regulatory limits can mean warnings from regulators, disrupted production, higher treatment costs, or wastewater that must be reprocessed before discharge.

However, before rushing to buy new equipment, sharply increasing chemical dosage, or blaming the WWTP operator, the more sensible first step is to find the source of the problem. In many cases, high COD is not caused by one major issue, but by small leaks, process changes, or a treatment system that is becoming unstable.

Here are five of the most common sources of high COD problems in factories.

1. Production Process Leaking into Drains

This is one of the most common causes, but it is often noticed too late. Raw materials, semi-finished products, process liquids, oil, sugar, starch, milk, organic solvents, or leftover mixtures can enter drains because of spills, leaking valves, loose hoses, tank overflow, or the habit of washing production areas directly into floor drains.

The problem is that these materials usually carry a high organic load. Even a small amount entering wastewater can sharply increase COD levels. A WWTP that was previously stable may suddenly receive a load far beyond its original design capacity.

The first areas to check are wet-process areas: material transfer points, filling, mixing, equipment washing, tank areas, and piping routes. Do not only look at the WWTP. In many high COD cases, the real source is on the production floor.

2. Excessive or Uncontrolled Cleaning Chemicals

Cleaning in place, sanitation, machine washing, and floor cleaning can contribute significantly to COD. Detergents, surfactants, alkalis, acids, sanitizers, and certain cleaning agents can make wastewater more difficult to treat, especially when discharged in high concentrations over a short period.

The problem becomes worse when cleaning schedules overlap with peak production hours. As a result, the WWTP receives organic wastewater, cleaning chemicals, pH changes, and high flow at the same time.

Factories need to check the types of chemicals used, actual dosages in the field, cleaning frequency, and disposal methods. Sometimes the issue is not the chemical itself, but excessive use because operators want things to be “cleaner” without a clear dosage standard.

3. Poor Equalization

The equalization tank is often seen merely as a holding tank. In fact, its function is important for balancing flow, COD concentration, pH, temperature, and wastewater characteristics before the next treatment stage.

If equalization does not work properly, the WWTP receives wastewater in unstable patterns. One hour the load is low, the next hour it spikes. This condition makes physical-chemical treatment, DAF, and biological processes difficult to stabilize.

Check whether tank capacity is sufficient, mixing is working, transfer pumps are not too aggressive, and no concentrated wastewater bypasses directly to the next unit. Poor equalization often causes operators to chase problems at the final stage, even though the root cause is at the front end.

To understand the relationship between COD and other parameters such as BOD, you can read this discussion: COD vs BOD: Differences and How to Measure Them.

4. Shock Load from Production

Shock load occurs when the WWTP receives a sudden wastewater load far higher than normal conditions. The causes may include product changeovers, failed batches, disposal of expired materials, major cleaning activities, tank draining, or overtime production without treatment adjustment.

The signs are usually visible from a spike in influent COD, rapid pH changes, increased foam, odor, sludge changes, or outlet water that begins to fail standards.

Shock load needs to be managed through operational control, not only by reacting at the end of the process. Factories should have procedures for concentrated wastewater: holding it first, diluting it gradually, processing it separately, or feeding it slowly into equalization.

5. Unstable DAF or Biological Process

If the factory uses DAF, its performance strongly affects the COD load entering the next treatment process. Unstable DAF performance may be caused by incorrect coagulant-flocculant dosage, unsuitable pH, air pressure problems, poor recycle flow, or sludge that is not removed routinely.

As a result, oil, grease, TSS, and organic particles are not removed optimally. COD load that should have been reduced at the early stage passes into the next unit instead. To understand its role, see this article: Dissolved Air Flotation: How It Works and Its Benefits in Wastewater Treatment.

In biological systems, high COD can occur when microorganisms are under stress. The causes may include extreme pH, nutrient deficiency, low DO, toxic shock from chemicals, sludge that is too old, or organic load that exceeds system capacity. When the biological process is already unstable, simply increasing chemical dosage usually does not solve the root problem.

Priority Actions Before Investing in New Equipment

Before buying additional units, take cost-efficient steps first. Audit wastewater sources from production, separate concentrated wastewater, control cleaning chemicals, improve equalization, record the timing of COD spikes, and evaluate DAF or biological performance using daily data.

New equipment investment only makes sense when the source of the problem is clear, the actual wastewater load has been calculated, and the existing system has been proven insufficient. Without that, new equipment will only receive the same problem at a higher cost.